1. Field of the Invention
The present invention relates to vehicle control systems. More particularly, this invention relates to controls in electric vehicles of the types used as tow tractors or "tuggers" and low-lift transporters or "pallet trucks" and which are designed for use by an operator either riding or walking beside the vehicle, such as in filling or "picking" orders. Such vehicles are referred to herein generically as electric rider vehicles.
2. Description of the Prior Art
A variety of electric rider vehicles have been developed which also provide the capability for the operator to operate the machine from a walking position. Typically, the operator must attempt to utilize rider controls for machine movement while walking with the vehicle.
Such rider vehicles are commonly utilized in two different movement modes. One mode is for transport movement over a substantial distance, such as to or through a storage warehouse. In such operation, the vehicle usually is operated at higher speeds in order to allow a means of quick transportation of the rider, the vehicle and any payload. The other movement mode is when the operator is picking orders from warehouse storage. Upon location of a particular order component or part, the operator will step off the drive vehicle to "pick" the component from storage. When picking several components from the same general warehouse area, it may be advantageous for the operator to move the vehicle while walking alongside the vehicle, rather than remounting and driving.
The ability to operate the vehicle from the walking position is thus a desirable feature of such vehicles, for example where they are being used for "order picking." However, there is also a need for safety and control during that operation.
One safety feature is provided in such vehicles through the use of deadman controls. Deadman controls disable the propulsion power and apply the brakes on the drive vehicle in the absence of the operator's weight on the platform or a foot pedal. Safety can also be provided through speed limitations in the movement of the vehicle.
In an order picking movement mode, often it is preferable that the vehicle be capable of operator-free coasting for a short distance, e.g. three to six feet. This allows the operator who walks along the side of the vehicle to release the vehicle while in motion and to pick an order, then turn around and place the package on a cart which is being towed by the tractor or on a platform or pallet carried at the rear of the truck, e.g., on a low lift fork. The cart, platform or pallet is then beside the operator due to the intervening coasting movement. Similarly, following operation in the first movement mode, it may be advantageous for the operator to have the option of releasing the forward speed control while stepping off the machine at the desired order picking position. Ideally, the vehicle would then coast three to six feet, allowing the operator to pick the package and deposit the package on the cart which is then beside the operator. However, the utilization of deadman controls which apply the brake in the absence of an operator on the operator's platform eliminates the aforementioned features from conventional vehicles.
As a result of the practical needs of the order picker utilizing an electric rider vehicle, it is desirable that the drive vehicle be capable of multi-speed operation and yet be capable of providing a coasting mode to enable the operator to step off while picking orders and not cause the application of the deadman brake. Further, it is desirable to provide for control from a walking position, preferably with free-coasting capability, for the order picker who walks along beside the vehicle.
In some prior art vehicles attempts have been made to meet these needs by allowing operation of the rider handle controls from a walking position. However, many of these machines permit high travel speeds of the machine when operated from a walking position, which can present an undesirable operational hazard.